This invention relates generally to methods and apparatus for removing contaminants from aqueous systems, and more specifically relates to methods and filtration devices for removing undesired contaminants from bilgewater discharge.
Over the past two decades, U.S. regulations dealing with oily bilgewater discharge for all types of vessels have grown increasingly stringent. Even the presence of a visible oil sheen is deemed objectionable under the Uniform National Discharge Standards (xe2x80x9cUNDSxe2x80x9d). Environmental technology has struggled to keep pace, but until recently no removal method has been capable of eliminating sheen and extracting harmful contaminants from bilgewater.
The Federal Water Pollution Actxe2x80x94also known as the Clean Water Actxe2x80x94accordingly proscribes even the appearance of a visible sheen on the water, punishable by a $5,000 penalty. More specifically, the act xe2x80x9cprohibits the discharge of oil or oily waste into or upon the navigable waters of the United States or the waters of the contiguous zone if such discharge causes a film or sheen upon, or causes a sludge or emulsion beneath the surface of the water.xe2x80x9d
Further, under Sections 4301 (a) and (c) of the Oil Pollution Act of 1990, the fine for failing to notify the appropriate federal agency of a discharge has increased from a maximum of $10,000 to a maximum of $250,000 for an individual and $500,000 for an organization. The discharge of oil regulation, or xe2x80x9csheen rule,xe2x80x9d establishes the following criteria for determining a harmful oil spill:
Discharges that cause a sheen or discoloration on the surface of a body of water;
Discharges that violate applicable water quality standards; or
Discharges that cause a sludge or emulsion to be deposited beneath the surface of the water or on adjoining shorelines.
The sheen rule applies to both petroleum and non-petroleum oilsxe2x80x94e.g., vegetable oil.
The discharge regulations also have been toughened for U.S. military vessels. The National Defense Authorization Act of 1996 amended Section 312 of the Federal Water Pollution Control Act to require the Secretary of Defense and the administrator of the U.S. Environmental Protection Agency (EPA) to develop UNDS for vessels of the armed forces for xe2x80x9cdischarges, other than sewage, incidental to normal operationxe2x80x9d. Previously, this section only addressed the regulation of sewage.
From an environmental perspective, the increased regulatory activity in bilgewater discharge limits is warranted. The cumulative effect of vessels ranging from small recreational boats to large surface ships dumping even small amounts of bilgewater could wreak damage upon fragile aquatic ecosystemsxe2x80x94and likely has already done so.
According to nature of discharge (NOD) reports obtained from the U.S. Navy, the composition of untreated bilgewater is a varying assortment of oil and grease, oxygen-demanding substances, and organic and inorganic materials. These materials, the reports say, include volatile organic compounds, semi-volatile organic compounds, inorganic salts and metals. The common metals collected in bilgewater samples include arsenic, copper, cadmium, chromium, lead, mercury, selenium and zinc, while organics include benzene, isomers of hexachlorocyclohexane, ethyl benzene, heptachlor, heptachlor expoxide, napthalene, phenols, pthalate esters, toluene, trichlorobenzene and trichloroethane.
The primary sources of these contaminants are vessel propulsion systems and auxiliary systems that use fuels, lubricants, hydraulic fluid, antifreeze, solvents and cleaning chemicals. Certain waste streams such as steam condensate, boiler blowdown, drinking fountain water, and sink drainage located in various machinery spaces can also drain to the bilge.
In worst-case scenarios, environmentally irresponsible vessel operators have dealt with excess bilgewater by dumping it overboard. Others have tried to hide the telltale sheen with emulsifiers, though the damage is still done.
Currently, commercial and military surface ships primarily employ two different methods in dealing with bilgewater treatment and removal. Many of these vessels use oil water separator systems to reduce the oil content of bilgewater prior to overboard discharge. Most of these large vessels also have an onboard systems for collecting and transferring bilgewater to a holding tank for later removal and disposal on shore.
Now in accordance with the present invention, it has been found that the compositions disclosed in the present inventor""s U.S. Pat. Nos. 5,437,793; 5,698,139; 5,837,146; and 5,961,823 (all of which disclosures are hereby incorporated by reference) have extremely strong affinities for the aforementioned contaminants in oily bilgewater; and that when oily bilgewater streams containing these noxious contaminants are passed through filtration media incorporating these inventive compositions, the contaminants are immobilized at the media, as a result of which concentration levels of the contaminants in the filtrate may be reduced to very low values, in some instances below detectable limits in a single pass. Use of the invention not only enables ready removal from the bilgewater of oils, greases and the like, but as well removal of pernicious slightly soluble organic compounds such as benzene, toluene, xylene, halogenated hydrocarbons, ethoxylated glycols, etc. These noxious contaminants are among the more difficult compounds to remove from water, and indeed most are carcinogenic. The solubility of the foregoing substances renders most prior art physical separation methods ineffective and causes formation of stable and pseudostable oily emulsions (miscelle size of 400 micrometers or less) which also don""t respond well to gravity separation due to neutral buoyancy. Among the metal ions which additionally may be removable by the methods and apparatus of the invention are those of cadmium, chromium, copper, lead, nickel, zinc, arsenic, silver, and mercury.
In accordance with the present invention, the oily bilgewater is passed through one or more filters incorporating the principles of the invention, prior to the bilgewater being actually discharged from the vessel. The filter or filters may simply be placed directly in the bilgewater discharge line, e.g. downstream of the bilgewater pump effecting the discharge flow. In a test of a typical such installation, and using a dwell time of one second and a flow rate of 20 gallons per minute, a filter in accordance with the invention reduced all contaminants to below detectable limits (BDL) at various percentages of oil contamination. The test results included removal of all sheen and visible discharge. The methods of the invention have the ability to remove from the bilgewater most mixed emulsions and lipohilic and hydrophilic organic compounds, in addition to many chelated and colloidal metals.
Filter configurations incorporating the above described compositions (hereinafter referred to as xe2x80x9cabsorbent compositionsxe2x80x9d) may be based on various water permeable substrates, such as shredded, spun or otherwise configured polypropylene or shredded or spun cellulose, which substrates are infused or otherwise treated with the absorbent compositions, which are then cured. These substrates may then be packed or otherwise disposed in a cartridge or canister filter; or can be formed into cured and infused bag filters which can be emplaced in canisters through which the contaminated bilgewater is flowed. Similarly the said absorbent compositions can be incorporated into or upon other filtering substrates and media, such as paper, including compressed pulp materials, particulate porous foamed plastics, mineral particulates such as perlite and vermiculite, and particulate, fibrous or porous ceramic or porous (e.g. sintered) metal substrates and media.